1. Field of the Invention:
The invention relates generally to power drive systems for self-propelled crop harvesters and, more particularly, to an improved hydrostatic drive for the self-propelled chassis of the harvester and for the crop handling elements on a header coupled to the chassis.
2. Prior Art:
It is known in the art to power the crop handling components of a crop harvesting machine through hydraulic motors. Examples are shown in U.S. Pat. No. 3,613,336 and in a brochure entitled Hesston Hydro-Static Model 6600 Windrower and designated HS-1873 and published by Hesston Corporation of Hesston, Kansas. Those skilled in the art would refer to the drive of the patent as "hydraulic" whereas the drive of the machine illustrated in the brochure would be called "hydrostatic" (a specific type of hydraulic drive). By whatever art terms the power drives are referred to, the basic problem resides in designing a system for controlling a drive which provides safe and effective control of the vehicle in conjunction with considerations of manufacturing and maintenance costs.
It is believed that the prior art in this area may have evolved in the following manner: Having placed the basic pump and motor components in the vehicle chassis, the system designer then began to consider what kind of control system could be created to be compatible with the basic layout and position of the pumps and motors. Whether the design sequence is as above in every case or not, the resulting machines include a rather complex array of links, levers, arms, gears, cables and the like for controlling the power drive of the vehicle. Of course, the greater the complexity the greater the cost and probability of premature repair or replacement.
U.S. Pat. No. 3,065,700 shows a unified (and thus somewhat simplified) control for two pumps, but including an expensive governor-controlled, power-operated speed control system.